The present invention relates to a vehicle body structure, and more particularly to a load-bearing space frame, and to a method of manufacturing thereof.
A space frame for a motor vehicle, comprising a plurality of elongated metal structural members having axially uniform cross-sections joined together by a plurality of interconnecting metal castings, is known from the prior art, e.g. as disclosed in U.S. Pat. No. 4,735,355. Specially designed castings, having a saddle portion with a contour matching a portion of the cross-section of the structural member, ensure a joint of two or several structural members at a given angle. Furthermore, the saddle portion and a tubular portion of the casting are provided with outer peripheral edges lying along the outer surface of the structural members, where a welded bead is deposited along these edges in order to reinforce the joint areas.
U.S. Pat. No. 4,355,844 discloses another load-bearing structure for a motor vehicle based on tubular members (girders) joined together by connectors composed of shell elements of thin sheet metal, provided with longitudinal flanges having a plurality of tubular connection stubs. Another construction of the vehicle space frame is disclosed in European Patent Application No. 0146716. This frame comprises hollow shapes extruded from light metal and forming elongated structural members, connectors of different shapes or configurations adapted to the shape of the structural members and optionally provided with protruding/recessing parts in order to incorporate other parts of the vehicle body and finally plate (blanket) parts of different materials (light metals, steel, plastic) to complete the frame structure.
All the disclosed space frames are assembled from a large number of individually designed and dimensioned parts and members. The obvious disadvantages of such space frames are the large number of joints, the necessity to provide costly, specially made connectors and secondary use of reinforcing means in order to achieve satisfactory stiffness and strength of the frame. All these factors adversely affect the vehicle weight, the assembly cost of the space frame, as well as the of the frames ability to absorb certain amounts of energy for attaining predictable collision performance.